1. Field of the Invention
The invention concerns apparatus in which electrical connection is made to a mass of carbon granules and particularly carbon transducers such as microphones and transmitters.
2. Description of the Prior Art
The common telephone handset has for many years depended upon a transmitter in which mechanical vibrations are converted into electrical variations on a carrier current by means of contacting carbon granules. Traditionally, an electrode in this transmitter has consisted of a gold plated contact, often a contact which was first shaped and subsequently electroplated.
Recent severe increases in gold prices have provoked studies designed to replace this gold plated electrode. Many alternatives have been studied, but none has been generally accepted.
For example, substitution of gold by palladium or an alloy of palladium-silver, so promising in so many applications, has failed. Failure of this and other materials is ascribed to attack by a variety of agents present in the hostile environment resulting from sulfur and other gases released by carbon.
An alternative which has proven successful in the instance of certain electrode structures, notably the back electrode in the same transmitter, is not useful. Carbon cannot be shaped and its use would necessitate expensive redesign.